Manually operated caulking guns have been designed for dispensing caulking compounds and other viscous or plastic material from disposable tubes. The caulking guns typically include a trigger mechanism which forces a drive piston on a push rod against a piston in the tube to dispense the selected quantity of caulking compound or other material.
One such manual caulking gun is manufactured by the COX Company under the tradename WEXFORD. The trigger mechanism in the COX gun includes a hand grip die-cast with a frame, and a trigger pivotally connected to the frame. The trigger is adapted to be pivoted towards the grip, which forces a flange on the trigger to drive a washer on a push rod off-center. The washer cocks and grabs the push rod, thereby urging the push rod forwardly within a tube holder. A drive piston connected to the push rod is thereby forced against the end of a tube in the tube holder to dispense the viscous or plastic material. At the end of the trigger stroke, the trigger is released, and a spring uncocks the washer and biases the washer and the trigger back into their initial position, while a locking lever prevents the push rod from moving rearwardly.
Conventional replaceable tubes for caulking compounds and other viscous or plastic material include a casing, a tube cap, and a plastic tube piston which together define a cavity for the material. The tube piston is adapted to be urged against the material and dispense the material through a nozzle over the cap. Tubes typically contain about 10 fluid oz. of material, but other sizes, such as 30 fluid oz., are available. The tubes are disposable and are designed to be replaced when exhausted, as compared to bulk caulking guns which have a dispensing chamber adapted to be filled directly with the viscous or plastic material. A typical replaceable tube designed for caulking compound is manufactured by The Glidden Company under the tradename MACCO Adhesives.
Other dispensers for caulking compounds or other material use compressed air instead of a manually applied force to dispense the material from the tube. The compressed air reduces the manual effort necessary to dispense the material. For example, Wills et al, U.S. Pat. No. 3,983,947, discloses a caulking gun having a push rod in a chamber urged forwardly by compressed air entering the rear of the chamber. A trigger is adapted to urge a valve ball out of its seat within a valve chamber to allow the compressed air to flow around the valve ball and into the piston chamber.
Similarly, Collar, U.S. Pat. No. 3,980,209, discloses a caulking gun for bulk dispensing of plastic or viscous material, wherein a piston in a forward barrel is connected by a shaft to a piston in a rear barrel. During dispensing of the material, a trigger is adapted to engage a trigger piston and allow compressed air to flow through an air passage to the rear of the forward barrel. The compressed air forces the forward piston against the material, which is thereby dispensed through a nozzle in the caulking gun.
Additionally, Mackal, U.S. Pat. No. 4,441,629, discloses a caulking gun wherein a CO.sub.2 cartridge supplies compressed gas through a valve assembly to the rear portion of the caulking gun cylinder. The compressed gas is forced against the caulking tube piston, which thereby applies pressure to the caulking compound and dispenses the compound through the caulking tube nozzle.
These caulking guns however, are not without drawbacks. For example, when compressed air or gas is applied directly against the piston of the caulking tube, the piston has a tendency to tilt, and the compressed air or gas can leak around the piston and channel through the caulking compound. The channeling causes sputtering at the nozzle of the caulking tube and a degradation of the caulking product.
Moreover, compressed air from an air compressor is relatively inexpensive when compared to compressed gas from a CO.sub.2 cartridge. Accordingly, caulking guns using compressed air from a compressor can more readily afford to exhaust a good portion of the air during use, such as through the movement of valves and leaks in the valve assembly.
However, using a dispensing device with the more portable, but relatively more expensive liquid CO.sub.2 cartridge presents some important economic considerations. In particular, each CO.sub.2 cartridge contains a limited amount of liquid CO.sub.2. The gas which is produced from the liquid CO.sub.2 must therefor be used as efficiently as possible for dispensing the viscous or plastic material.